A "thrifty gene" has been proposed as a genetic defect that would predispose the Pima Indians to store energy very efficiently and account for the high prevalence of obesity in this population. To determine if such genetic differences exist, we have constructed a human respiratory chamber at the Clinical Diabetes and Nutrition Section. This chamber will allow us to measure energy expenditure in Indians and Caucasians over prolonged periods of time to determine if the Indians truly have an abnormality of energy expenditure. In addition, we are determining the thermogenic response of the Indians to different stimuli-food, norepinephrine, exercise and insulin.